In mobile communication networks, such as for example in 3G networks (3G=3rd Generation) or in 4G networks (4G=4th Generation networks), great effort is undertaken to increase the throughput of data that can be exchanged with multiple mobile UEs (UE=user equipment) sharing the radio resources available for one or multiple cells of the network. One cell or one transmission point serves multiple users such that the multiple users served by one cell or by one single transmission point need to share the available radio resources. One single base station, also denoted as NodeB or eNodeB, may serve multiple remote radio heads, antennas or antenna arrays, each of the antennas or of the antenna arrays being utilized to send data to and to receive data from a particular area. Several mobile units communicating simultaneously with the same antenna or the same antenna array share the radio resources or the available radio channels of the antenna.
In this respect, the term transmission point shall in the following be understood to be a device or an entity with which user equipments of the network communicates via a radio channel, such that all user equipments communicating with the same transmission point are able to share the radio resources or available radio channels. That is, the user equipments communicating with the same transmission point potentially interfere with each other in terms of bandwidth, cross-talk or the like. Apart from that potential interference, which can be handled by a serving transmission point alone, also two or more radio channels provided by two or more transmission points may interfere with each other at the location of the user equipment or a mobile station such as to decrease the achievable data rate for that user equipment or that mobile station. Such interference typically occurs at the border of the areas irradiated or served by neighboring transmission points, that is, at the borders of the areas or cells associated to the transmission points.
In order to account for the problem of such inter-transmission point interference and/or to increase the throughput of an existing network infrastructure, CoMP transmissions (CoMP=Coordinated MultiPoint) may be performed. In order to do so, two or more transmission points within a cluster of transmission points may share the information about the quality and the signaling parameters of some or of all of the UEs communicating via the individual transmission points of the cluster. Various approaches exist to enhance a network's efficiency or throughput by employing CoMP transmission in the uplink as well as in the downlink. Among these, for example, coordinated scheduling/beam forming for the downlink where user data is only available or transmitted at one transmission point, the so-called serving transmission point or serving cell, but user scheduling and beam forming decisions are made with coordination among the individual transmission points of a cluster. In joint processing CoMP user data is transmitted to user equipment via multiple transmission points. The so called joint transmission achieves an enhancement of the throughput by transmitting data of a data channel to a user equipment simultaneously via multiple transmission points.
All coordinated multipoint downlink implementations, however, require the knowledge of the transmission characteristics or the quality of the radio channels between all transmission points in the cluster potentially serving a particular user equipment and the respective user equipment. The transmission points being monitored by the user equipment and hence serve as candidates for establishing a downlink transmission are in the following also called the set of transmission points used for measurements. To this end, the user equipment is required to feed back some channel feedback information to the transmitter side. In the particular example of an LTE system (LTE=Long Term Evolution), for example pre-coding direction information is transmitted via a PMI (PMI=Pre-coding Matrix Indicator), while a CQI (CQI=Channel Quality Indicator) corresponds to a preferred MCS (MCS=Modulation and Coding Scheme). Enabling the network or some transmission scheduling entity therein to perform scheduling decisions for CoMP in order to exploit the available network bandwidth to a high extent, however, requires that the network or the scheduling entity is continuously informed about the channel feedback information of all potential radio channels between all transmission points that are a candidate for a downlink transmission to a particular UE.